The invention relates generally to refractory compositions. More specifically, the invention relates to refractory compositions suitable for closing the tapholes of blast furnaces and the like and to specialty compositions such as plastic and ramming mixes.
In the past, compositions for plugging the tapholes of blast furnaces, as well as refractory carbon-containing specialty compositions such as plastic, ramming mixes, gunning mixes and mortars, have generally contained a refractory filler and a carbonizable binding material. Coal tar has previously been employed as such a binding material and continues to represent one of the most economical binding agents. However, in both taphole plugging and specialty applications, coal tar bonded refractory compositions have been recognized as generating substantial quantities of noxious fumes during firing. These fumes pose air contamination and occupational health hazards and have been recognized as carcinogenic.
Efforts have been made in the past to replace the coal tar binding materials. For example, U.S. Pat. No. 4,072,531 issued to Funabiki et al. discloses a blast furnace taphole plugging composition including, inter alia, a lignin-modified phenolformaldehyde condensation product as a replacement for some or all of the tar binding material. In reference to prior art efforts to substitute conventional phenolic resins for the coal tar binder in similar compositions, Funabiki et al. notes that conventional phenolic resins solidify prematurely in the applicator and are disadvantageously expensive.
U.S. Pat. No. 4,022,739, issued to Bove also discloses a binder for taphole plugging compositions which does not generate noxious fumes to the degree experienced with coal tar. The binder of Bove comprises a mixture of a high boiling hydrocarbon derivative and a synthetic resin, which may be a formo-phenolic resin having resorcinol moecules in the polymer chain. In this regard, the use of resorcinol-formaldehyde polymers as temporary binders for refractory materials is well-known. U.S. Pat. No. 3,007,805, issued to Cline and U.S. Pat. No. 2,938,807, issued to Andersen both disclose the use of phenol-formaldehyde and resorcinol-formaldehyde resins as carbonizable binders for refractory bodies.
Use of phenol-formaldehyde and resorcinol-formaldehyde polymers as the binding material in non-aqueous taphole mix compositions and refractory specialties does not entirely solve the fume problem. More specifically, these polymers commonly contain free formaldehyde. As noted in U.S. Pat. No. 3,917,558 issued to Gardikes et al., the formaldehyde vapors generated during curing are unpleasant, irritaing and pose a health hazard to persons continually exposed to such vapors. Moreover, these polymers may contain 5-10% free phenol, which may also vaporize during curing and thus generate toxic fumes. With respect to refractory specialties in particular, the fumes from organic solvents employed with prior art synthetic resin binders were hazardous to both manufacturing employees and employees using the specialty material.